1. Field of the Invention
The present invention relates to a recording disk apparatus such as a magnetic disk apparatus employed as an exterior storage device for a computer system.
2. Description of the Prior Art
A hard disk drive unit (HDD) representing a magnetic disk apparatus, for example, employs a magnetic disk surrounding a rotation axis which is driven by a spindle motor. When information is recorded or read out, the magnetic disk is driven for rotation with respect to a magnetic head.
The magnetic disk is fixed between a clamp and a flange formed on the rotation axis near the base end. The clamp is fixed at the tip end of the rotation axis so as to urge the magnetic disk against the flange.
In fixing the clamp on the rotation axis, a plurality of screws are employed to fix the plane body of the clamp at the tip end of the rotation axis. The screws are arranged on an imaginary circle concentric to the rotation axis. The plane body is urged strongly against the rotation axis in the screw bore areas, while the urging force is weakened in the intermediate areas between the screw bore areas along the imaginary circle.
Variation in the tightening pressure along the imaginary circle causes undulation on the plane body along the imaginary circle, since the plane body at the screw bore areas sinks more than that at the intermediate areas between the screw bore areas. This undulation of the plane body is transferred to the magnetic disk which the periphery of the plane body contacts, so that the magnetic disk also suffers from undulation. The undulation of the magnetic disk causes undesirable effects when the magnetic head is intended to record or read out information in or out of the magnetic disk. In particular, the recent trend to reduce the flying height of the magnetic head above the magnetic disk in an HDD, for example, has brought difficulty unpreventing the magnetic head from interfering with the magnetic disk.
It is an object of the present invention to provide a recording disk apparatus capable of eliminating undulation of a recording disk by preventing deformation of a clamp in contact with the recording disk. It is another object of the present invention to provide a clamp capable of realizing such a recording disk apparatus.
According to a first aspect of the present invention, there is provided a recording disk apparatus comprising: a rotation axis having a flange: a recording disk surrounding the rotation axis; a clamp urging the recording disk against the flange; screws disposed along an imaginary circle concentric to the rotation axis so as to fix a plane body of the clamp at a tip end of the rotation axis; and a rigidity reduction mechanism reducing rigidity of the plane body at an intermediate area relative to screw bore areas, the intermediate area being defined between the screw bore areas along the imaginary circle.
When the clamp is fixed by the screws at the tip end of the rotation axis, tightening pressure is effected on the clamp at the screw bore areas. Since the rigidity of the plane body at the intermediate area is reduced relative to the screw bore areas in the above recording disk apparatus, the tightening pressure can equally be effected at the intermediate area, so that the clamp sinks toward the tip end of the rotation axis equally at the screw bore and intermediate areas. Therefore, the clamp is prevented from deformation so that undulation can be suppressed in the disk in contact with the clamp.
The aforementioned rigidity reduction mechanism may comprise an annular wall raised from a surface of the plane body, and a recess formed on the annular wall at a top face in said intermediate area. The rigidity of the plane body as a whole can be reinforced by the annular wall, while the rigidity at the intermediate area can relatively be reduced by the recess. Therefore, the clamp can be prevented from deformation as mentioned above.
The recess may comprise a tapered surface continuous, from the top surface. Employment of the tapered surface between the top surface and the recess enables employment of a press in forming the clamp. In this case, the clamp may be formed from metallic material such as aluminum or a stainless steel. It is preferable to select the metallic material in consideration of strength and rigidity of the clamp, and thermal expansion coefficient.
The recess may be defined by a curved surface. For example, formation of the curved surface between the bottom of the recess and the tapered surface and between the top surface of the annular wall and the tapered surface serves to avoid concentration of stress in such connection areas. As a result, the screws for fixing the clamp at the rotation axis can maintain the tightening pressure in a longer term.
In addition, the rigidity reduction mechanism may comprise an annular wall raised from a surface of the plane body, and a recess formed on the annular wall at a side (outer or inner) face in said intermediate area. The rigidity of the plane body as a whole can be reinforced by the annular wall, while the rigidity at the intermediate area can relatively be reduced by the recess. Therefore, the clamp can likewise be prevented from deformation. Moreover, the annular wall maintains continuous inner or outer surface so that an inner space within the annular wall can be reliably isolated from the outer space around the clamp. Accordingly, a balancer disposed within the inner space of the annular wall cannot fall off from the clamp toward the surrounding disk.
Further, the rigidity reduction mechanism may comprise a through hole formed in the plane body in the intermediate area. The through hole likewise serves to reduce the rigidity at the intermediate area, so that the clamp can be suppressed from deformation.
The rigidity reduction mechanism may comprise a large through hole in the middle of a pair of the screw bores, and a small through hole disposed in an area between the large through hole and the screw bore to have a diameter smaller, than that of the large through hole. Variation in the diameter of the through holes enables variation in rigidity of the plane body in the circumferential direction, leading to fine adjustment for the deformation of the clamp.
Furthermore, according to a second aspect of the present invention, there is provided a recording disk apparatus comprising: a rotation axis having a flange; a recording disk surrounding the rotation axis; a clamp urging the recording disk against the flange: screws disposed along an imaginary circle concentric to the rotation axis so as to fix a plane body of the clamp at a tip end of the rotation axis; and an annular wall raised from a surface of the plane body surrounding the screws to have a thickness larger than that of the plane body.
With the above recording disk apparatus, the rigidity of the clamp may be reinforced by the annular wall surrounding the screw bore areas, while the rigidity is relatively reduced at the screw bore areas in the plane body. Therefore, when tightening pressure is effected from the screws, it is absorbed around the screw bore areas in the plane body. The plane body can be prevented from deformation at the periphery surrounding the screw bore areas, where the annular wall is formed. Thus, the disk faces of the recording disk can be maintained flat.
It should be noted that the aforementioned clamps may be distributed dependent or independent of a recording disk apparatus.